The present invention is generally directed to high fidelity color toner compositions and processes thereof. More specifically, the present invention is directed to processes from forming colored toners and developed images therefrom and which toners and images possess high color fidelity properties, for example, maximized chroma while minimizing pigment loading and deleterious effects associated therewith on the physical properties of the toner and toner images, for example, conductivities, resin reinforcement, image fix, image gloss, fuser roll loading, and the like concerns.
A problematical requirement of pigmented toners, and particularly of pigmented toners with small average particle sizes, for example, from about 1.0 to about 10.0 microns, is that high pigment loading, for example, from about 10 to about 20 weight percent pigment of the total weight of the toner composition, is required to achieve high chroma values. However, high pigment loading is accompanied by a host of problems which can adversely impact the properties of either or both the toner particles and toner images thereof.
A collateral problem associated with aforementioned high pigment loading is the difficulty of satisfactorily dispersing the pigment in the toner resin. This leads to unwanted absorption bands, inferior color quality, increased image scatter, lower chroma, poor transparency projection quality and the like problems.
Another major problem encountered with toners at high pigment loading is a phenomena known in the art as "resin reinforcement", which refers to very high toner melt viscosity that is imparted to the toner matrix and is believed to result from mechanical reinforcement of the resin by the pigment particles. Since resin reinforcement is a function of pigment loading, resin reinforcement occurs whether the toner is prepared by, for example, conventional comminutive processing or where prepared by toner particle growth schemes, also known as "chemical toner" processes, such as emulsion aggregation, when the pigment loading exceeds about 10 weight percent of the total weight of the toner. Resin reinforcement leads to the aforementioned deleterious effects. For fine toners, for example, with a number average particle size diameter of from about 2 to about 8 microns, desired for high fidelity color imaging, high pigment loadings, for example, from about 20 to about 30 weight percent, are believed necessary to achieve adequate color saturation at reduced toner pile heights and toner mass per unit areas. Thus, for 3 micron toners, for example, pigment loadings of about 20 weight percent and above are indicated. A way to avoid the reinforcing properties of pigments is to substitute a dye compound for the pigment. In this approach however, high dye loading or levels can plasticize the resin and can produce lower glass transition temperatures and corresponding lower blocking temperatures.
The aforementioned problems are unsatisfactory for black-and-white electrostatographic and especially color applications. The present invention overcomes the aforementioned problems.
The compositions and development processes of the present invention are useful in many electrostatographic applications, for example, in xerographic printers and copiers, and especially in color xerographic systems.